Still loving this. Can I make a suggestion about writing tecnique.
In this section >>> “Me?” Jack grabbed the mug that slid from Ianto’s fingers before it could hit the ground. “Gwen is in danger because of me?”<<< it is Ianto speaking but because you've put Jack's name in there it reads as him. It took me a couple of goes to see what you meant.
It could have been written .. 'Me?' Ianto's hand open in shock. Jack grabbed....
Just a marvelous story. I've still got another chapter to read so I'm off to do that right now.